Advanced renewable energy harvesting

ABSTRACT

The power of DC electrical sources is combined onto a DC buss, such that each source behaves independently from any other source attached to the buss. In one embodiment, a converter module is attached to each of a plurality of solar photovoltaic panels and its output is attached in a parallel manner to a common buss that forms the input to a DC AC inverter. The converter module includes a Maximum Power Point Tracking component that matches the output impedance of the panels to the input impedance of the converter module. The converter also includes a communication component that provides parametric data and identification to a central inverter. Data generated by each converter module is transmitted over the power line or by wireless means and is collected at the inverter and forwarded to a data collection and reporting system.

CROSS REFERENCE TO RELATED APPLICATIONS

This patent application claims the priority and benefit of, and is acontinuation of, U.S. patent application Ser. No. 13/371,213, filed Feb.10, 2012, to be issued as U.S. Pat. No. 9,041,252, which is itself acontinuation of U.S. patent application Ser. No. 12/338,610, filed Dec.18, 2008, issued as U.S. Pat. No. 8,138,631, which is itself anonprovisional of U.S. provisional patent application No. 61/016,365,Packaging, Assembly, and Mounting of Photovoltaic Solar Panels, filedDec. 21, 2007, the entirety of each of which are incorporated byreference herein in their entireties for all purposes.

BACKGROUND OF THE INVENTION

1. Technical Field

This invention relates generally to the field of renewable energy powermanagement. More specifically, this invention relates to the powerproduction, power conversion, and power management of DC energy sourcessystems.

2. Description of the Related Art

Coal-burning energy produces some of the highest greenhouse-gasemissions of any of the fuels in widespread use. The United Statescurrently uses coal-burning fuel to provide about half of the country'selectric power. The United States is continually striving to find cheapand efficient ways to generate its own clean energy in an effort toimprove the environment and achieve energy independence.

The shift to more energy-efficient policies can also create new jobs. InCalifornia, for example, nearly one and a half million jobs have beencreated between 1977 and 2007 as a result of energy-efficiency policies.The state's policies improved employee compensation by $44.6 billion.

Solar power is one of the cleanest sources of energy available. Sunlightis captured from the sun in the form of electromagnetic radiation andgenerated into a direct current (DC) using photovoltaic (PV) cells. ThePV cells are made of semiconductors, e.g. silicon and are fabricated inthe form of semiconductor arrays, films, inks, or other materials. Theindividual PV cells can be aggregated, interconnected together, and thenpackaged into solar panels of some size and shape and within a rugged,environmentally sealed enclosure that is suitable for physical mountingand/or installation on residences, businesses, earth-mounted poles,vehicles, roof-tops, and other locations.

The DC has a current (I) and voltage (V). The relationship between thecurrents produced by a solar panel or series-connected group of panelsand the output voltage may be plotted or graphed on an XY axis as afamily of IV curves. The solar panel output current I bears a directrelationship to the spectral power density or level of sunlight(spectral irradiance) illuminating the panel at a given time, and maychange dramatically relative to small changes in irradiance. In thetypical case where some number of such solar panels are seriesconnected, the solar panel with the lowest level of current flow willdictate or set the current flowing throughout the series circuit. Panelsconnected in series can lose up to 60% of their energy as a result ofbeing limited by the worst-performing panel.

FIG. 1 illustrates one type of problem associated with series-connectedsolar panels that are limited by the solar panel with the lowest levelof current flow. On a sunny day, all the panels may receive the samelevel of sunlight. If there are any clouds 100 in the sky, however, theymay partially obscure a panel 110. So even though some of the panels maybe receiving almost all sunlight 120, because the system is seriesconnected 130, the current flow is limited by the worst performing panel110.

The optimal power of the solar panel array is obtained by incorporatinga maximum power point tracking (MPPT) algorithm to optimize the overallpower available for harvesting to maintain the power output at themaximum level possible for a given system or string current. Usually theelectronics and any software necessary to implement this MPPT functionare incorporated into the implementation of the system's DC-to-ACconversion function (DC-to-AC inverter) in grid-connected PV systems oras a component of a storage battery charging and control system foroff-grid solar applications. Global MPPT algorithms provide only theaverage operating point of the total string, not the maximum. Anoptimized system provides per panel MPPT functionality to account forindividual panel optimum operating points as well as variations in paneloperating characteristics.

String inverters must be able to accommodate strings of varying numbersof interconnected panels and a wide variety of panel types. Because ofthese variations, a traditional DC-to-AC inverter used in aseries-connection system is subjected to high stress and heat levelsresulting in a one percent failure rate within the first six months.

Various methods have been implemented to maximize the energy output. InU.S. Pat. No. 7,158,395, for example, an outer voltage feedback loop wasdeveloped to track trends in increasing power sources and adjust theMPPT algorithm accordingly. This approach suffers from a limitation onoverall or maximum system power that may be harvested at any point intime due to the series connection of panels, and the requirement thatthe current flowing through such a series circuit cannot be any greaterthan that produced by the panel with the smallest output current.

U.S. Publication Number 2008/0097655 discusses calculating a separateMPPT for each solar panel to optimize power production. [0026] Thepanels supply power to the bus separately. [0026] Information about eachpanel is transmitted on top of the bus to a management unit, which isconnected to a network using TCP/IP protocol. [0020]-[0021] Themanagement unit provides monitoring and control for system components.

The design of series-connected panel systems is time consuming. Allpanels must be from the same manufacturer and be of the same model orpower rating, multiple strings of series-connected panels must be of thesame length or contain the same number of panels, panels with differentorientation to the sun must be treated as separate subsystems, andadd-ons to an existing installation are treated as additions of acompletely separate subsystem.

The maintenance of series-connected panel systems is alsotime-consuming. When a system is connected in series, any defects in oneof the panels will cause the entire system to fail. This is the samedefect that occurs in a string of Christmas lights when one of thelights breaks. To locate the defective panel, a technician must test thepanels separately. As a result, the cost of hiring a technician to visitthe site and locate the defective panel is prohibitively expensive.

SUMMARY OF THE INVENTION

In one embodiment, the invention provides a separate DC DC boostconverter and maximum power point tracking (MPPT) component for eachenergy gathering source. In one embodiment, the energy gathering sourceis a solar panel. The MPPT component matches the output impedance of thepanels to the input impedance of the boost converter to maximize thepower for each panel. The individual converter component boosts outputvoltage of the panels to a voltage that is high enough to minimizetransmission wire losses while efficiently inverting the DC to an ACvoltage.

Using a parallel method of interconnecting a number of solar panels witha constant voltage output to a DC buss eliminates the problemsassociated with using a string of series-connected solar panels. Thissystem allows the current from each individually optimized panel to sumtogether to produce a current that is independent of the efficiency orsolar conversion capability of any one panel. As a result, the systemovercomes the Christmas light problem because the system continues tofunction even with broken panels.

This creates the freedom to use different solar panels with different IVcharacteristics, panels constructed from different PV technologies, andpanels installed at different orientations relative to the sun. In oneembodiment, additional panels are added to the installation at any time.In another embodiment, other power sources, e.g. fuel cells, batteries,wind turbines, etc. are coupled to individual converter components andattached to the DC buss for either point of use or DC to AC conversionfor use or sale back to the utility company.

In another embodiment, a communications component is coupled to eachpanel for monitoring. The monitoring system provides information such aspanel ID, temperature, voltage, current, power, efficiency, diagnostics,etc. The monitoring system is for individual users or a company thatharvests the energy. This information helps technicians immediatelyidentify malfunctioning panels and maximizes the efficiency of eachpanel. The monitoring system also provides information regarding theoutput and efficiency of the complete system and alerts the producer ofunderperformance or problematic power production.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram that illustrates a prior-art system ofseries-connected solar panels;

FIG. 2A is an illustration of a solar panel system according to oneembodiment of the invention;

FIG. 2B is an illustration of a solar panel system connected in parallelaccording to one embodiment of the invention;

FIG. 3 is an illustration of a solar panel system including panelmodules, an inverter, and a monitoring system according to oneembodiment of the invention;

FIG. 4 is a more detailed illustration of the solar panel systemaccording to one embodiment of the invention; and

FIG. 5 is an example of the power obtained from solar panels as afunction of time according to one embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

The invention is a system and method for harvesting electrical energyfrom solar panels and for converting it into energy. Each solar panel iscoupled to a converter component, which is connected in parallel to a DCpower buss. The converter component includes a DC DC boost converter forboosting the panel's output voltage for DC transmission on a power buss,an MPPT component for maximizing energy transfer between the panel andthe transmission buss, and a communication component for receivinginformation about the panel and transmitting the information to a userand a company that manages the panels. The power buss is connected to aninverter for changing the power from a direct current (DC) to analternating current (AC) and generating an AC that is in phase with thepower grid.

One embodiment of the system for each solar panel is illustrated in FIG.2A. In one embodiment, the power is obtained from solar panels 200. Inanother embodiment, the power is obtained from another energy source,e.g. wind, hydroelectric, fuel cell, battery, etc. or a combination ofthese sources. Persons of ordinary skill in the art will understand thatalthough the system is discussed with reference to solar panels, thesystem architecture is easily applied to other energy sources.

Each solar panel 200 is coupled to an individual converter component205. The converter component 205 receives the electrical power outputfrom the solar panel 200. The converter component 205 comprises a DC DCboost converter 210, a MPPT component 215, and communication component220. The MPPT component 215 determines the maximum power point using aMPPT algorithm. The boost converter 210 converts the electrical poweroutput to a higher voltage and lower current for transmission via a DCpower buss 225 to the inverter 230. The communication component 220collects information about the solar panel 200, e.g. panelidentification, voltage, current, power, temperature, diagnostics, etc.

The inverter 230 converts the electrical power from DC to AC to betransferred to the power grid 235 or a battery 235 for storage.Information about the solar panel 200 and converter module 205 collectedby the communications component 220, e.g. panel ID, temperature,voltage, current, power, efficiency, diagnostics, etc. are transmittedto a corresponding communication component 240 that forms part of theinverter 230. These components are discussed in more detail below.

FIG. 2B illustrates one embodiment of the invention where all the panelsare connected in parallel. The panels can be produced from differentmanufacturers and constructed using different technologies, e.g.crystalline silicon, thin film, amorphous silicon, etc. andspecifications. Panels connected in parallel function independently ofeach other. As a result, the panels are installed in the best positionand at the best angle for harvesting energy. The solar panels 200 arecoupled to individual converter components 205. The energy istransferred to the inverter 230 via a DC power buss 225.

FIG. 3 is an illustration of the system that includes transmission ofthe data obtained by the communications component 220 from the inverter230 to users via the Internet 300. The monitoring data is sent toinstallers, producers, consumers, utility companies, etc. This data canbe reviewed from anywhere, for example, on a desktop 305, a laptop 310,or even on a handheld device 315.

FIG. 3 also illustrates that the different panels produce differentamounts of power. For example, some produce 167 watts, some produce 188watts, etc. In addition, the panels are not all part of the same array.The off-array panel 305 is connected to the power buss 225 in the samemanner as the other panels 200.

Circuit Block Diagram

The circuit block diagram for the system is illustrated in FIG. 4according to one embodiment of the invention. The DC DC boost converter210 comprises an input filter 400, an auxiliary power supply 405, aflyback switching network 410, an output filter and common mode choke415, an ORing diode 420, and enable/disable operating sensors 435. Theconverter component 205 receives a variable DC input voltage and currentand converts it to an output power at a voltage level determined by theDC buss 225 as set by the inverter 230. The input filter 400 performselectromagnetic interference filtering from the flyback switchingnetwork 410 back to the panel 200. The auxiliary power supply 405provides internal power for the various circuits within the convertercomponent 205.

The output filter and common mode choke component 415 provideselectromagnetic interference filtering out to the DC buss 225 and alsoprevents the communication signal from being absorbed by the filtercomponents. The output is then connected to the DC buss via an ORingdiode 420, which prevents power backfeed from the DC buss 225 to theconverter component 205.

The MPPT component 215 comprises an MPPT control 425 and a pulse widthmodulator (PWM) 430. The MPPT control 425 determines the panel 200output impedance and matches the input impedance of the flybackswitching network 410 via the PWM 430 for maximum power transfer. TheMPPT control 425 includes an autoranging feature that allows panels ofdiffering output voltages and currents to be used on the same buss 225.The output of the panel 200 is sensed and the appropriate operatingrange is selected. In one embodiment, the flyback switching network 410boosts the input voltage until power begins flowing onto the DC buss225. Output power to input power efficiencies of greater than 95% havebeen realized using this topology.

The enable/disable operating sensors component 435 performs circuitfunction tests such as temperature, voltage and current to ensureoperation within the converter component's 205 safe operatingspecifications. Power up sequencing includes checking for an enablesignal from the inverter 230, via the DC buss 225 and the communicationscomponent 220 before enabling the PWM 430 and the flyback switchingnetwork 410. When disabled, the converter component 205 is in the offstate and has zero output voltage and current. The enable/disablecomponent 435 also internally limits the output voltage to preventrunaway and destruction of the circuit. In one embodiment, this voltagelimit is set at 375V. If the enable signal from the inverter 230 islost, the PWM 430 and flyback switching network 410 are immediatelydisabled and the excess voltage and current are bled off in a controlledmanner.

In one embodiment, the communications component 220, i.e. the physicallayer is capacitively coupled 440 to the DC buss 225 via a radiofrequency (RF) carrier for power line communication to the inverter 230.Other physical layer embodiments include inductive coupling to the DCBuss 212 as well as wireless communications between the convertercomponent 205 and the inverter 230. In one embodiment the communicationsprotocol is implemented using a controller area network (CAN) bus. Aperson of ordinary skill in the art will recognize which embodiment isappropriate for each system architecture.

Regardless of the input voltage and current, in this embodiment theoutput is always the same so that multiple converter components 205 canbe connected in parallel to sum the power of each panel. The powercontrol loop is unregulated so that the DC buss 225 determines theoutput voltage of the converter components 205. In this manner, allparalleled converter components 205 regulate to the buss voltage, whichis set by the inverter 230 according to its operating requirements.

By connecting panels 200 in parallel and performing per panel maximumpower point operation, each panel operates as an independent powerproducer from any other panel within the system. In this way, power lossdue to temperature effects, shading, panel fault or disconnect, islimited to the affected panel and the power loss is minimized.Conversely, in conventional string topologies the panels are connectedin a series string and the system performance is determined by the leastperforming panel. In traditional topologies a single panel fault ordisconnect brings down the entire string.

FIG. 5 is a plot of voltage as a function of time. The DC voltage 500and the AC voltage 510 were plotted over a 24 hour period. The areaunder the AC curve represents the total power 520. This graphdemonstrates that as a result of the MPPT control 425, energy can berecovered during the initial start-up phase and when panels experienceshading, because the panels are connected in parallel instead of theconventional series string topology.

There are many advantages associated with per panel voltage boost.First, panels of any size and operating characteristic can beincorporated into a single system since the output of each panel is nownormalized via the converter component 205. Second, panels can be placedin virtually any location or configuration, which significantly reducessystem design and installation time and costs. Lastly, additional panelscan be added to an existing system without requiring complete systemredesign and reinstallation. In one embodiment solar panels areintegrated with other power sources, e.g. fuel cell, wind turbines,batteries, etc. onto a single DC buss 225. Each power source has its ownconverter componenet 205, which results in maximum system integrationfor either grid tie or off-grid applications.

DC AC Inverter System

The inverter 215 converts the electrical DC, i.e. voltage and currentoutput from a DC energy source, e.g. solar panels, fuel cells,batteries, or wind turbines, to an AC i.e. voltage and current outputand transfers the AC to a utility power grid 235 or battery 235. When DCsources are used to supplement grid power, the grid tie inverterperforms the DC to AC conversion and regulatory synchronization to theutility power grid. Surplus power generated by the system is sold backto the utility company depending on the system's location. For off-gridapplications, energy harvested from solar panels and other renewableenergy sources is used to supply power and is stored in systems, e.g.batteries for use when the energy sources are unavailable.

In one embodiment, the inverter 230 is a less complex and smallerinverter than traditional models because the DC buss 225 voltage isboosted by the converter component 205 to an optimized level andtherefore does not need an input DC voltage level converter or levelshifting transformer at the inverter's output. The smaller inverter isless expensive, creates a more reliable system, and significantlyimproves power harvesting.

The inverter 230 consists of an optimized modulator, power factorcorrection, anti-islanding, and grid synchronizing circuitry. It alsocontains a communication component 240 that provides data transferbetween the inverter 230 and the converter component 205 coupled to thepanel 200. The inverter 230 may also contain a secondary communicationscomponent that sends the system data to web based services fordistribution to applicable stakeholders, e.g. the system owner,installer, financer, etc.

The communications layer can be used to gather operational data from thesystem, as well as control the operation of each converter component205. For example, in one embodiment, the inverter 230 sends a power goodsignal to the converter module 205 to confirm that the system isproperly connected and operating within normal parameters. The powergood signal is typically sent shortly after the system is powered on. Ifthe power good signal is not received by the communication component205, the boost converter 210 is disabled to prevent damage to thevarious components and to provide a safe environment for maintenance oremergency conditions where the system must be turned off.

Operational data can be formatted to comply with user or utility reportrequirements. Remote control of the system is possible in order todisable the entire system in the event of an emergency requiring allsystems off and safe. Thus, in one embodiment, the communicationscomponent 240 receives input from a user. The communications component240 can also be used to monitor and control other appliances and systemswithin the local circuit network.

As will be understood by those familiar with the art, the invention maybe embodied in other specific forms without departing from the spirit oressential characteristics thereof. Likewise, the particular naming anddivision of the members, features, attributes, and other aspects are notmandatory or significant, and the mechanisms that implement theinvention or its features may have different names, divisions and/orformats. Accordingly, the disclosure of the invention is intended to beillustrative, but not limiting, of the scope of the invention, which isset forth in the following Claims.

1. A system for harvesting maximum power from a plurality of energysources comprising: a DC buss for transmitting DC to a load, whereinsaid DC buss operates at a DC buss voltage set by said load; a pluralityof energy receiving components each configured for outputting directcurrent (DC) from energy received from at least one energy sourceindependently from each other, wherein each energy receiving componentfrom among said plurality of energy receiving components furthercomprises a converter component comprising: a boost converter forupconverting said DC from said energy receiving component to said DCbuss voltage; wherein each of said at least one converter component isconnected to said DC buss in parallel with others of said at least oneconverter component; and wherein said boost converter in each respectiveconverter component operates said converter component as an independentpower producer by converting a variable DC voltage and current receivedfrom said energy receiving components to an output power at a voltagedetermined by the DC buss as set by the load.
 2. The system of claim 1,further comprising: an inverter for inverting electrical energy fromdirect current (DC) to an alternating current (AC); and a powercapturing source for receiving said AC from said inverter.
 3. The systemof claim 1, further comprising: a maximum power point tracking (MPPT)component for real time determination of an output impedance of saidenergy receiving component; said MPPT component varying an operatingpoint of said boost converter to match said impedance of said DC fromsaid energy receiving component to maximize transfer of power.
 4. Thesystem of claim 1, said converter component further comprising: an inputfilter for filtering electromagnetic interference and reducing voltageand current ripple backfeed from said DC to said energy receivingcomponents; a switching network for upconverting a voltage of said DCfrom said energy receiving components to said DC buss voltage; an outputfilter for filtering electromagnetic interference and reducing said DCvoltage and current ripple to said DC buss; an ORing component forpreventing backfeed from said DC buss into said converter component; anda common mode choke for facilitating power line communications via radiofrequency (RF) signals superimposed onto said DC buss.
 5. The system ofclaim 2, said MPPT component further comprising: a MPPT control forgenerating a maximum power point for said DC; and a pulse widthmodulator for matching an input impedance of said converter component toan output impedance of said energy receiving source.
 6. The system ofclaim 1, further comprising: a communication component for gatheringinformation about said energy receiving components, said communicationcomponent transmitting a signal over a power line by generating radiofrequency signals that represent digital signals.
 7. The system of claim4, wherein said information gathered by said communication componentcomprises at least one of: temperature, voltage, power, current,efficiency, and diagnostics of said energy receiving components.
 8. Thesystem of claim 6, wherein said communication component receives inputs.9. The system of claim 8, said communication component comprising: meansfor transmitting instructions to said converter component to deactivatesaid converter component's output in response to any of user input, lossof an enable signal from an inverter, disconnection from said DC buss,and disconnection of said inverter from said DC buss.
 10. The system ofclaim 1, wherein said energy receiving components comprise solar panels.11. The system of claim 1, wherein said energy receiving componentsreceive energy from at least one of solar power, wind energy,hydroelectric energy, a fuel cell, and a battery.
 12. The system ofclaim 1, said inverter further comprising: a communications componentthat transmits information about said system using a wirelesstransmission.
 13. A method for harvesting energy, the method comprisingthe steps of: transmitting, with a DC buss, to a load, wherein each ofsaid DC buss operates at a DC buss voltage set by said load; capturingenergy with a plurality of energy receiving components, wherein saidcaptured energy is output as a direct current (DC), and wherein eachenergy receiving component captures energy independently from oneanother by configuring each energy receiving component with a convertercomponent comprising a boost converter for upconverting said DC fromsaid energy receiving component to said DC buss voltage; upconverting,by said boost converter, said DC from each said energy receivingcomponent; wherein said boost converter is connected to said DC buss inparallel to others of said at least one boost converter; wherein saidboost converter in each respective converter component operates saidconverter component as an independent power producer by converting avariable DC voltage and current received from energy receiving componentto an output power at a voltage determined by the DC buss as set by theload.
 14. The method of claim 13, further comprising: inverting, with aninverter, electrical energy from direct current (DC) to an alternatingcurrent (AC), wherein said inverter is configured with a thresholdvoltage; and said inverter transmitting said AC to a power capturingsource.
 15. The method of claim 13, further comprising: determining, bya maximum power point tracking (MPPT) component within each of said atleast one boost converter, an output impedance of at least one energyreceiving component by varying an operation point of said boostconverter to match said impedance of said DC from said energy receivingcomponent.
 16. The method of claim 13, further comprising the steps of:filtering electromagnetic interference and reducing voltage and currentripple backfeed from said DC to said energy receiving components aninput filter; upconverting said DC voltage from said energy receivingcomponents to said DC buss voltage with a switching network; filteringelectromagnetic interference and reducing voltage of said DC and currentripple to said DC buss with an output filter; preventing backfeed fromsaid DC buss into said converter component with an ORing component; andfacilitating power line communications via radio frequency (RF) signalssuperimposed onto said DC buss with a common mode choke.
 17. The methodof claim 15, further comprising the steps of: generating a maximum powerpoint for voltage of said DC with an MPPT control; and matching an inputimpedance of said converter component to an output impedance of saidenergy receiving component with a pulse width modulator.
 18. The methodof claim 13, further comprising the step of: gathering information aboutsaid energy receiving components with a communications component, saidcommunication component transmitting a signal over a power line bygenerating radio frequency signals that represent digital signals. 19.The method of claim 18, wherein said information gathered by saidcommunication component comprises at least one of temperature, voltage,power, current, efficiency, and diagnostics of said energy receivingcomponents.
 20. The method of claim 18, further comprising the step of:said communication component receiving inputs from a user.